On 2013/6/17 1:21, Oleg Nesterov wrote:
> perf_trace_buf_prepare() + perf_trace_buf_submit() make no sense
> if this task/CPU has no active counters. Change kprobe_perf_func()
> and kretprobe_perf_func() to check call->perf_events beforehand
> and return if this list is empty.
>
> For example, "perf record -e some_probe -p1". Only /sbin/init will
> report, all other threads which hit the same probe will do
> perf_trace_buf_prepare/perf_trace_buf_submit just to realize that
> nobody wants perf_swevent_event().
>
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
Good point, I think we also need to change other places in below patch.
After applied the patch, perf_tp_event() function call reduced a lots
when using task based perf tracing.
-----------------------------------
tracing: Avoid perf_trace_buf_*() if ->perf_events is empty
Signed-off-by: zhangwei(Jovi) <jovi.zhang...@huawei.com>
---
include/trace/ftrace.h | 5 ++++-
kernel/trace/trace_syscalls.c | 10 ++++++++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 19edd7f..5d340f5 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -659,6 +659,10 @@ perf_trace_##call(void *__data, proto)
\
int __data_size; \
int rctx; \
\
+ head = this_cpu_ptr(event_call->perf_events); \
+ if (hlist_empty(head)) \
+ return; \
+ \
perf_fetch_caller_regs(&__regs); \
\
__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
@@ -679,7 +683,6 @@ perf_trace_##call(void *__data, proto)
\
\
{ assign; } \
\
- head = this_cpu_ptr(event_call->perf_events); \
perf_trace_buf_submit(entry, __entry_size, rctx, __addr, \
__count, &__regs, head, __task); \
}
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 8f2ac73..28debf4 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -553,6 +553,10 @@ static void perf_syscall_enter(void *ignore, struct
pt_regs *regs, long id)
if (!sys_data)
return;
+ head = this_cpu_ptr(sys_data->enter_event->perf_events);
+ if (hlist_empty(head))
+ return;
+
/* get the size after alignment with the u32 buffer size field */
size = sizeof(unsigned long) * sys_data->nb_args + sizeof(*rec);
size = ALIGN(size + sizeof(u32), sizeof(u64));
@@ -571,7 +575,6 @@ static void perf_syscall_enter(void *ignore, struct pt_regs
*regs, long id)
syscall_get_arguments(current, regs, 0, sys_data->nb_args,
(unsigned long *)&rec->args);
- head = this_cpu_ptr(sys_data->enter_event->perf_events);
perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
}
@@ -629,6 +632,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs
*regs, long ret)
if (!sys_data)
return;
+ head = this_cpu_ptr(sys_data->exit_event->perf_events);
+ if (hlist_empty(head))
+ return;
+
/* We can probably do that at build time */
size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
size -= sizeof(u32);
@@ -649,7 +656,6 @@ static void perf_syscall_exit(void *ignore, struct pt_regs
*regs, long ret)
rec->nr = syscall_nr;
rec->ret = syscall_get_return_value(current, regs);
- head = this_cpu_ptr(sys_data->exit_event->perf_events);
perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
}
--
1.7.9.7
--
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